Method and apparatus for converting alcohols to hydrocarbons

ABSTRACT

Apparatus and method of utilization for controlling exothermic reactions such as the conversion of methanol to hydrocarbons are discussed. More particularly, the arrangement of apparatus comprising heat exchange tubes and open end baffle tubes for maintaining the hydraulic diameter within restricted limits during contact between vaporous reactant and a fluid bed of catalyst is discussed.

BACKGROUND OF THE INVENTION

The application of fluidized catalyst techniques for effecting chemicalreactions embodying the distribution of heat and/or the disposal ofundesired reaction heat has long been accepted as a major processingtool of the petroleum and chemical industry. For example, it has beenproposed to use the fluidized catalyst technique in the exothermicreactions of Fischer-Tropsch synthesis, the known Oxo process as well asothers for the disposal of generated heat. In the fluid catalyticcracking of hydrocarbons, the fluid catalyst conveys heat generated inthe catalyst regeneration zone to the hydrocarbon conversion zonewherein the conveyed heat is given up by converting hydrocarbons admixedtherewith to form more desirable hydrocarbon products such as gasoline.In these various fluidized catalyst operations, disposal of the reactionheat has been accomplished by different techniques including thetransfer of heat to cooling coils, and indirect heat exchange withfluidized catalyst particles or reactant feed streams and productstreams.

The conversion of lower alcohols, such as methanol, to intermediateether products followed by conversion of the ether product to one or acombination of products comprising olefins and/or aromatics has been thesubject of several patents. Such patents include U.S. Pat. Nos.3,928,483; 3,931,349; 3,969,426; 3,998,899; 4,013,732; 4,035,430;4,044,061; 4,046,825; 4,052,479; 4,058,576; 4,062,905; 4,071,573;4,076,761; 4,118,431 and 4,138,440. These patents and others have beenconsidered in the preparation of this application.

Some other patents given consideration include U.S. Pat. Nos. 2,493,526;2,571,380; 2,627,522; 2,920,940 and 3,151,944.

SUMMARY OF THE INVENTION

This invention relates to an arrangement of apparatus and its method ofutilization for effecting the conversion of lower alcohols such asmethanol, ethanol, and propanol, ether derivatives thereof and mixturesof alcohols and ethers in the presence of fluid catalyst particles of aspecial class of crystalline zeolites to form hydrocarbons includinggasoline boiling range hydrocarbons characterized as olefinic and/oraromatic hydrocarbons.

More particularly, the present invention is directed to an arrangementof apparatus for effecting the conversion of methanol in the presence offluid catalyst particles comprising a special zeolite characterized asproviding a pore opening of at least 5 Angstroms, a silica/alumina ratioof at least 12 and a Constraint Index within the range of 1 to 12. Thearrangement of apparatus comprises in combination a cylindrical reactorhousing a generally upflowing fluidized relatively dense mass ofcatalyst particles initially contacted by vapor and/or liquid loweralcohols, ether derivatives thereof and related oxygenates or a mixturethereof. The charge may be methanol alone, in admixture with ether (DME)and related oxygenates including oxygenates of Fischer-Tropschsynthesis.

The reactor is provided with a plurality of vertically arranged steamgeneration tubes in combination with juxtapositioned special gas bubbledispersing baffle tubes confined particularly within the most denseportion of the fluid mass of catalyst particles within the lower portionof the reactor. A catalyst regenerator is provided adjacent the reactorin combination with associated subsystems provided for preheating themethanol feed, reactor effluent cooling and recovery, a catalystregeneration system, a system for effecting heat-up of the reactor andrelated piping means between vessels which are straight or semicircularconduit means for conveying catalyst particles between the reactor andthe regenerator. The steam tubes and the baffle tubes above mentionedfor restricting gas bubble growth means which are in a specificembodiment, 4 inch nominal diameter tubes hung vertically from supportbeams. The baffle tubes are open at the top and bottom. They areprovided with a plurality of staggered elongated slots in the wall ofthe baffle tube at spread apart intervals to permit the transfer ofcatalyst particles and vaporous material into and through the slots inthe baffle tubes without substantial flow restriction except to suppressgas bubble growth. A sufficient number of vertical steam tubes andbaffle tubes are arranged adjacent to one another in the fluid mass ofcatalyst particles to provide an equivalent hydraulic diameter betweencatalyst particles and vaporous material restricted to within the rangeof 4 to 8 inches and preferably to about 6 inches. In one specificembodiment of the apparatus arrangement herein described, it iscontemplated utilizing a catalyst inventory for the reactor andregenerator arrangement of about 933,000 pounds based on a reactor sizeproviding a catalyst bed depth of about 40 feet in a 35 foot diameterreactor. It is also contemplated using a catalyst bed depth less than 40feet, such as 20 or 30 feet. The specific apparatus arrangement and sizeherein described are designed for processing about 52,640 BPD of crudedistilled methanol containing up to about 4% water and producing, underthe selected operating conditions, about 13,400 BPD of C₅ + gasolineboiling range products plus light olefins, paraffins, isoparaffins andnaphthenes as secondary products. Alkylation of olefinic secondaryproducts may be accomplished in separate equipment known in the art.

The crystalline zeolites utilized herein are members of a novel class ofzeolitic materials which exhibit unusual properties. Although thesezeolites have unusually low alumina contents, i.e. high silica toalumina mole ratios, they are very active even when the silica toalumina mole ratio exceeds 30. The activity is surprising, sincecatalytic activity is generally attributed to framework aluminum atomsand/or cations associated with these aluminum atoms. These zeolitesretain their crystallinity for long periods in spite of the presence ofsteam at high temperature which induces irreversible collapse of theframework of other zeolites, e.g. of the X and A type. Furthermore,carbonaceous deposits, when formed, may be removed by burning at higherthan usual temperatures to restore activity. These zeolites, used ascatalysts, generally have low coke-forming activity and therefore areconducive to long times on stream between regenerations by burningcarbonaceous deposits with oxygen-containing gas such as air.

An important characteristic of the crystal structure of this novel classof zeolites is that it provides a selective constrained access to andegress from the intracrystalline free space by virtue of having aneffective pore size intermediate between the small pore Linde A and thelarge pore Linde X, i.e. the pore windows of the structure are of abouta size such as would be provided by 10-membered rings of silicon atomsinterconnected by oxygen atoms. It is to be understood, of course, thatthese rings are those formed by the regular disposition of thetetrahedra making up the anionic framework of the crystalline zeolite,the oxygen atoms themselves being bonded to the silicon (or aluminum,etc.) atoms at the centers of the tetrahedra.

The silica to alumina mole ratio referred to may be determined byconventional analysis. This ratio is meant to represent, as closely aspossible, the ratio in the rigid anionic framework of the zeolitecrystal and to exclude aluminum in the binder or in cationic or otherform within the channels. Although zeolites with a silica to aluminaratio of at least 12 are useful, it is preferred in some applications touse zeolites having higher silica/alumina ratios of at least about 30.In addition, zeolites as otherwise characterized herein but which aresubstantially free of aluminum, i.e. having silica to alumina moleratios of 1,600 and higher, are found to be useful and even preferablein some instances. Such "high silica" zeolites are intended to beincluded within this description. The novel class of zeolites, afteractivation, acquire an intracrystalline sorption capacity for normalhexane which is greater than that for water, i.e. they exhibit"hydrophobic" properties. This hydrophobic character can be used toadvantage in some applications.

The novel class of zeolites useful herein have an effective pore sizesuch as to freely sorb normal hexane. In addition, the structure mustprovide constrained access to larger molecules. It is sometimes possibleto judge from a known crystal structure whether such constrained accessexists. For example, if the only pore windows in a crystal are formed by8-membered rings of silicon and aluminum atoms, then access by moleculesof larger cross-section than normal hexane is excluded and the zeoliteis not of the desired type. Windows of 10-membered rings are preferred,although in some instances excessive puckering of the rings or poreblockage may render these zeolites ineffective.

Although 12-membered rings in theory would not offer sufficientconstraint to produce advantageous conversions, it is noted that thepuckered 12-ring structure of TMA offretite does show some constrainedaccess. Other 12-ring structures may exist which may be operative forother reasons and, therefore, it is not the present intention toentirely judge the usefulness of a particular zeolite solely fromtheoretical structural considerations.

Rather than attempt to judge from crystal structure whether or not azeolite possesses the necessary constrained access to molecules oflarger cross-section than normal paraffins, a simple determination ofthe "Constraint Index" as herein defined may be made by passingcontinuously a mixture of an equal weight of normal hexane and3-methylpentane over a sample of zeolite at atmospheric pressureaccording to the following procedure. A sample of the zeolite, in theform of pellets or extrudate, is crushed to a particle size about thatof coarse sand and mounted in a glass tube. Prior to testing, thezeolite is treated with a stream of air at 540° C. for at least 15minutes. The zeolite is then flushed with helium and the temperature isadjusted between 290° C. and 510° C. to give an overall conversion ofbetween 10% and 60%. The mixture of hydrocarbons is passed at 1 liquidhourly space velocity (i.e., 1 volume of liquid hydrocarbon per volumeof zeolite per hour) over the zeolite with a helium dilution to give ahelium to (total) hydrocarbon mole ratio of 4:1. After 20 minutes onstream, a sample of the effluent is taken and analyzed, mostconveniently by gas chromatography, to determine the fraction remainingunchanged for each of the two hydrocarbons.

While the above experimental procedure will enable one to achieve thedesired overall conversion of 10 to 60% for most zeolite samples andrepresents preferred conditions, it may occasionally be necessary to usesomewhat more severe conditions for samples of very low activity, suchas those having an exceptionally high silica to alumina mole ratio. Inthose instances, a temperature of up to about 540° C. and a liquidhourly space velocity of less than 1, such as 0.1 or less, can beemployed in order to achieve a minimum total conversion of about 10%.

The "Constraint Index" is calculated as follows: ##EQU1##

The Constraint Index approximates the ratio of the cracking rateconstants for the two hydrocarbons. Zeolites suitable for the presentinvention are those having a Constraint Index of 1 to 12. ConstraintIndex (C.I.) values for some typical materials are:

    ______________________________________                                                               C.I.                                                   ______________________________________                                        ZSM-4                    0.5                                                  ZSM-5                    8.3                                                  ZSM-11                   8.7                                                  ZSM-12                   2                                                    ZSM-23                   9.1                                                  ZSM-35                   4.5                                                  ZSM-38                   2                                                    TMA Offretite            3.7                                                  Clinoptilolite           3.4                                                  Beta                     0.6                                                  H-Zeolon (mordenite)     0.4                                                  REY                      0.4                                                  Amorphous Silica-Alumina 0.6                                                  Erionite                 38                                                   ______________________________________                                    

The above-described Constraint Index is an important and even criticaldefinition of those zeolites which are useful in the instant invention.The very nature of this parameter and the recited technique by which itis determined, however, admit of the possibility that a given zeolitecan be tested under somewhat different conditions and thereby exhibitdifferent Constraint Indices. Constraint Index seems to vary somewhatwith severity of operation (conversion) and the presence or absence ofbinders. Likewise, other variables such as crystal size of the zeolite,the presence of occluded contaminants, etc., may affect the ConstraintIndex. Therefore, it will be appreciated that it may be possible to soselect test conditions as to establish more than one value in the rangeof 1 to 12 for the Constraint Index of a particular zeolite. Such azeolite exhibits the constrained access as herein defined and is to beregarded as having a Constraint Index in the range of 1 to 12. Alsocontemplated herein as having a Constraint Index in the range of 1 to 12and therefore within the scope of the defined novel class of highlysiliceous zeolites are those zeolites which, when tested under two ormore sets of conditions within the above-specified ranges of temperatureand conversion, produce a value of the Constraint Index slightly lessthan 1, e.g. 0.9, or somewhat greater than 12, e.g. 14 or 15, with atleast one other value within the range of 1 to 12. Thus, it should beunderstood that the Constraint Index value as used herein is aninclusive rather than an exclusive value. That is, a crystalline zeolitewhen identified by any combination of conditions within the testingdefinition set forth herein as having a Constraint Index in the range of1 to 12 is intended to be included in the instant novel zeolitedefinition whether or not the same identical zeolite, when tested underother of the defined conditions, may give a Constraint Index valueoutside of the range of 1 to 12.

The novel class of zeolites defined herein is exemplified by ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, and other similar materials.

ZSM-5 is described in greater detail in U.S. Pat. Nos. 3,702,886 and3,941,871. The entire descriptions contained within those patents,particularly the X-ray diffraction pattern of therein disclosed ZSM-5,are incorporated herein by reference.

ZSM-11 is described in U.S. Pat. No. 3,709,979. That description, and inparticular the X-ray diffraction pattern of said ZSM-11, is incorporatedherein by reference.

ZSM-12 is described in U.S. Pat. No. 3,832,449. That description, and inparticular the X-ray diffraction pattern disclosed therein, isincorporated herein by reference.

ZSM-23 is described in U.S. Pat. No. 4,076,842. The entire contentthereof, particularly the specification of the X-ray diffraction patternof the disclosed catalyst, is incorporated herein by reference.

ZSM-35 is described in U.S. Pat. No. 4,016,245. The description of thatcatalyst, and particularly the X-ray diffraction pattern thereof, isincorporated herein by reference.

ZSM-38 is more particularly described in U.S. Pat. No. 4,046,859. Thedescription of that catalyst, and particularly the specified X-raydiffraction pattern thereof, is incorporated herein by reference.

It is to be understood that by incorporating by reference the foregoingpatents to describe examples of specific members of the novel class withgreater particularity, it is intended that identification of the thereindisclosed crystalline zeolites be resolved on the basis of theirrespective X-ray diffraction patterns. As discussed above, the presentinvention contemplates utilization of such catalysts wherein the moleratio of silica to alumina is essentially unbounded. The incorporationof the identified patents should therefore not be construed as limitingthe disclosed crystalline zeolites to those having the specificsilica/alumina mole ratios discussed therein, it now being known thatsuch zeolites may be substantially aluminum-free and yet, having thesame crystal structure as the disclosed materials, may be useful or evenpreferred in some applications. It is the crystal structure, asidentified by the X-ray diffraction "fingerprint", which establishes theidentity of the specific crystalline zeolite material.

The specific zeolites described, when prepared in the presence oforganic cations, are substantially catalytically inactive, possiblybecause the intracrystalline free space is occupied by organic cationsfrom the forming solution. They may be activated by heating in an inertatmosphere at 540° C. for 1 hour, for example, followed by base exchangewith ammonium salts followed by calcination at 540° C. in air. Thepresence of organic cations in the forming solution may not beabsolutely essential to the formation of this type zeolite; however, thepresence of these cations does appear to favor the formation of thisspecial class of zeolite. More generally, it is desirable to activatethis type catalyst by base exchange with ammonium salts followed bycalcination in air at about 540° C. for from about 15 minutes to about24 hours.

Natural zeolites may sometimes be converted to zeolite structures of theclass herein identified by various activation procedures and othertreatments such as base exchange, steaming, alumina extraction andcalcination, alone or in combinations. Natural minerals which may be sotreated include ferrierite, brewsterite, stilbite, dachiardite,epistilbite, heulandite, and clinoptilolite.

The preferred crystalline zeolites for utilization herein include ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35 and ZSM-38, with ZSM-5 being particularlypreferred.

In a preferred aspect of this invention, the zeolites hereof areselected as those providing among other things a crystal frameworkdensity, in the dry hydrogen form, of not less than about 1.6 grams percubic centimeter. It has been found that zeolites which satisfy allthree of the discussed criteria are most desired for several reasons.When hydrocarbon products or by-products are catalytically formed, forexample, such zeolites tend to maximize the production of gasolineboiling range hydrocarbon products. Therefore, the preferred zeolitesuseful with respect to this invention are those having a ConstraintIndex as defined above of about 1 to about 12, a silica to alumina moleratio of at least about 12 and a dried crystal density of not less thanabout 1.6 grams per cubic centimeter. The dry density for knownstructures may be calculated from the number of silicon plus aluminumatoms per 1000 cubic Angstroms, as given, e.g., on page 19 of thearticle ZEOLITE STRUCTURE by W. M. Meier. This paper, the entirecontents of which are incorporated herein by reference, is included inPROCEEDINGS OF THE CONFERENCE ON MOLECULAR SIEVES (London, April 1967),published by the Society of Chemical Industry, London, 1968.

When the crystal structure is unknown, the crystal framework density maybe determined by classical pycnometer techniques. For example, it may bedetermined by immersing the dry hydrogen form of the zeolite in anorganic solvent which is not sorbed by the crystal. Or, the crystaldensity may be determined by mercury porosimetry, since mercury willfill the interstices between crystals but will not penetrate theintracrystalline free space.

It is possible that the unusual sustained activity and stability of thisspecial class of zeolites is associated with its high crystal anionicframework density of not less than about 1.6 grams per cubic centimeter.This high density must necessarily be associated with a relatively smallamount of free space within the crystal, which might be expected toresult in more stable structures. This free space, however, is importantas the locus of catalytic activity.

Crystal framework densities of some typical zeolites, including somewhich are not within the purview of this invention, are:

    ______________________________________                                                     Void       Framework                                                          Volume     Density                                               ______________________________________                                        Ferrierite     0.28   cc/cc     1.76 g/cc                                     Mordenite      .28              1.7                                           ZSM-5, -11     .29              1.79                                          ZSM-12         --               1.8                                           ZSM-23         --               2.0                                           Dachiardite    .32              1.72                                          L              .32              1.61                                          Clinoptilolite .34              1.71                                          Laumontite     .34              1.77                                          ZSM-4 (Omega)  .38              1.65                                          Heulandite     .39              1.69                                          P              .41              1.57                                          Offretite      .40              1.55                                          Levynite       .40              1.54                                          Erionite       .35              1.51                                          Gmelinite      .44              1.46                                          Chabazite      .47              1.45                                          A              .5               1.3                                           Y              .48              1.27                                          ______________________________________                                    

When synthesized in the alkali metal form, the zeolite is convenientlyconverted to the hydrogen form, generally by intermediate formation ofthe ammonium form as a result of ammonium ion exchange and calcinationof the ammonium form to yield the hydrogen form. In addition to thehydrogen form, other forms of the zeolite wherein the original alkalimetal has been reduced to less than about 1.5% by weight may be used.Thus, the original alkali metal of the zeolite may be replaced by ionexchange with other suitable metal cations of Groups I through VIII ofthe Periodic Table, including, by way of example, nickel, copper, zinc,palladium, calcium or rare earth metals.

In practicing a particularly desired chemical conversion process, it maybe useful to incorporate the above-described crystalline zeolite with amatrix comprising another material resistant to the temperature andother conditions employed in the process. Such matrix material is usefulas a binder and imparts greater resistance to the catalyst for thesevere temperature, pressure and reactant feed stream velocityconditions encountered in many cracking processes.

Useful matrix materials include both synthetic and naturally occurringsubstances, as well as inorganic materials such as clay, silica and/ormetal oxides. The latter may be either naturally occurring or in theform of gelatinous precipitates or gels including mixtures of silica andmetal oxides. Naturally occurring clays which can be composited with thezeolite include those of the montmorillonite and kaolin families, whichfamilies include the sub-bentonites and the kaolins commonly known asDixie, McNamee-Georgia and Florida clays or others in which the mainmineral constituent is halloysite, kaolinite, dickite, nacrite oranauxite. Such clays can be used in the raw state as originally mined orinitially subjected to calcination, acid treatment or chemicalmodification.

In addition to the foregoing materials, the zeolites employed herein maybe composited with a porous matrix material, such as alumina,silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, and silica-titania, as well as ternary compositions,such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia and silica-magnesia-zirconia. The matrix may bein the form of a cogel. The relative proportions of zeolite componentand inorganic oxide gel matrix, on an anhydrous basis, may vary widely,with the zeolite content ranging from between about 1 to about 99% byweight and more usually in the range of about 5 to about 80% by weightof the dry composite.

In the reactor arrangement herein described, the heat of reactionobtained by converting the methanol charge is absorbed by the catalystand in substantial measure by the steam tubes to produce 600 psig steam.This arrangement is intended to restrict the temperature to about 600°F. at the bottom of the bed and the fluid bed upper interface to withinthe range of 750° F. to about 775° F. Preferably the temperature in thereactor dilute phase is about 765° F. In this methanol conversion andoperating environment, it is contemplated achieving a methanolconversion of greater than 95% and preferably about 99.5% to minimizethe loss of difficult to recover methanol in process formed water. Atthe operating conditions defined, including a pressure restriction ofabout 32 psig at the bottom of the fluid mass of catalyst and about 25psig in the reactor dispersed catalyst phase and relying upon a nominalgas velocity of about 2 ft./sec., the density of the fluid mass ofcatalyst in the lower portion of the reactor is about 27 lbs/cu.ft.However, changes in gas velocity can change the bed density to higherand lower values. That is, when it is desired to change productselectivity to one of high olefin content as opposed to high aromaticsyield, the reaction time as a function of space velocity may be reducedby increasing the space velocity. On the other hand, aromatic formationis enhanced by a reduction in reactant space velocity to increase timeof contact between methanol reactant product and catalyst. A goodbalance in product selectivity between olefins, aromatics and paraffinsmay be had by a proper selection of reaction conditions.

It is known that large gas bubbles can form in a fluid catalyst systemand particularly large diameter, deep, fluidized catalyst beds even ifthe gas is first injected into the bed in an atomized condition or asvery small gas bubbles. It is believed that, to achieve the highmethanol conversion desired, above 95%, it is essential to severelyrestrict gas bubble growth to less than 24 inches, and preferably not toexceed about 8 inches. More preferably, the hydraulic diameter of thereactor or system should be restricted to within the range of 4 to 8inches when charging liquid or vaporized methanol for contact with thecatalyst at the bottom of the fluid bed of catalyst above a distributorgrid. To provide the hydraulic restrictions particularly preferredherein, the steam tubes are located vertically within the reactor, in aplurality of separate flow controlled bundles of tubes which can be shutoff or separately removed and replaced as required in the event of anymalfunctions. Thus, the steam tubes are vertically hung resemblingbayonet type heat exchange tubes attached to separate plenum chambers atthe top for adding water and removing high pressure steam respectively.In addition to the vertical steam tubes, a plurality of vertical baffletubes are provided therebetween which permit the free upflow ofcatalyst, reactants and reaction products while maintaining the reactorhydraulics as herein provided. The baffle tubes and the steam tubes arearranged uniformly over the reactor cross-section in a particular gridpattern or arrangement compatible with obtaining desired heat transfer,restriction of gas bubble growth and provide for recycling centrifugallyseparated catalyst by diplegs provided to various bed sections such as abottom, intermediate and/or upper portion of the most dense fluid massof catalyst in the reactor zone. It is preferred to discharge all diplegcatalyst adjacent the bottom of the bed. The reactor is provided witheight sets of three stage cyclones, in which arrangement all of thediplegs return separated catalyst to a bottom portion of the fluid bed.In addition, the portion of the vessel housing the cyclones may belarger in diameter than that portion of the vessel housing the mostdense fluid bed of catalyst and the heat exchange tubes. Suchenlargement by reducing reactant velocity will operate to also reducecatalyst entrainment into the cyclones.

The most dense bed of catalyst in the reactor vessel is supported abovea horizontal reactant inlet distributor grid perforated by amultiplicity of small diameter holes, about 11,000, providing relativelyuniform dispersal of vaporous and/or liquid methanol feed depending onpreheat at the bottom of the fluid bed of catalyst. In one particulararrangement, the small diameter feed inlet holes are about 0.25 inch indiameter. The pressure drop across the grid is sufficiently high toinsure uniform distribution of feed gas. It is contemplated providing anopen ended catalyst transfer tube extending from beneath the feed inletdistributor grid into the dispersed phase above the more dense fluid bedof catalyst. The top end of this open ended tube may be covered by aspaced apart inverted dish shaped plate to inhibit catalyst particlesfrom falling down into the tube. The bottom end of this catalysttransfer tube extends to a low point of the reactor vessel beneath thegrid and is provided with nozzle means for injecting a fluidizing gasfor conveying catalyst particles falling through the grid duringshutdown and before start-up from beneath the grid into the catalystsystem above the grid. Thus it is contemplated fluidizing the mass ofcatalyst passed to the reactor and in the reactor with an inert gas suchas nitrogen or other material suitable for the purpose to clear thechamber in the reactor beneath the grid of catalyst and to fluidize thecatalyst bed before injecting the methanol comprising charge underselected reaction conditions.

It will be quite apparent from the discussion herein presented that thearrangement of apparatus and the method of utilizing such apparatus aredesigned to accomplish dehydration of the alcohol charge to itscorresponding ether and effect conversion thereof to at least olefinsand/or aromatics. It is generally preferred, however, that the operationbe performed under conditions restricting the formation of durene.However, formation of some durene (1, 2, 4, 5 tetramethyl benzene) isnot fatally restricting to the process. This can be restricted bylimiting contact between formed aromatics and methanol charged.

In a reactor system particularly identified and its operation as hereinidentified, there is a large circulation of catalysts in the most densefluid catalyst bed, in the dispersed catalyst phase, between the denseand dispersed catalyst phases, as well as from the catalyst phasesthrough the cyclones and return to the lower portion of the catalyst bedby the cyclone diplegs. It is contemplated circulating from about 4 to 8million pounds per hour of catalyst in the specifically identifiedapparatus of this invention; the major portion of the cyclone separatedcatalyst flows through the diplegs of the first stage cyclones of whichthere are eight in the specific apparatus embodiment. The circulatedcatalyst will accumulate carbonaceous deposits thereon of a relativelyhigh order of magnitude, since only a portion of this circulatedcatalyst is withdrawn for passage to catalyst regeneration for burning aportion of the deposited carbonaceous material in a separate temperaturerestricted catalyst regeneration zone. In the methanol conversionapparatus arrangement, it is contemplated maintaining a high coke levelon internally circulated catalyst to preferentially promote the productof olefins and/or aromatics and isoparaffins. Thus the level of cokelike material (hydrocarbonaceous) retained on the catalyst may be withinthe range of 5 to 20% by weight and more preferably within the range of10 to 15% by weight. When operating to produce preferably olefiniccomponents, the olefins produced may be cyclized in a separatedownstream zone free of methanol, thereby permitting minimizing thetendency to produce aromatics higher boiling than gasoline boilingcomponents.

FIG. I is a diagrammatic sketch in elevation of the reactor apparatus ofthis invention comprising an arrangement of heat exchange tubes andbaffle tubes positioned in a lower portion of the reactor vessel andspaced vertically above a distributor grid means.

FIG. II is a diagrammatic sketch of a portion of cross-section A--A ofFIG. I, showing the relationship between heat exchange tubes, baffletubes and cyclone diplegs.

FIG. III is a view of a portion of the open end baffle tube showing thearrangement for slotting the tube wall.

Referring now to FIG. I by way of example, a reactor vessel 2 is shownprovided with heat exchange tube means 4 and baffle tube means 6. Thearrangement of these tube means with respect to one another is moreclearly shown by the cross-sectional view and arrangement of FIG. II.Furthermore, it is to be understood that there are several separate heatexchange steam generating tube bundles so that temperature control canbe separately exercised over different portions of the fluid catalystbed. The bottoms of the tubes are spaced above a feed distributor grid 8approximately 2 feet in a specific arrangement and sufficiently abovethe grid to be free of jet action by the charged feed through the smalldiameter holes in the grid. As mentioned above, the holes in the gridare 0.25 inch in diameter, and in one specific arrangement there areapproximately 11,000 holes. Provision is made for withdrawing catalystfrom above grid 8 as by conduit means 10 provided with flow controlvalve 12 for passage to catalyst regeneration not shown. Provision isalso made for passing the partially regenerated catalyst to the reactorfluid bed of catalyst as by conduit means 14 provided with flow controlvalve 16. The regenerated catalyst is charged to the catalyst bedbeneath the upper interface and sufficiently below to achieve goodmixing in the fluid bed. Since the amount of regenerated catalyst passedto the reactor is small by comparison, the temperature of theregenerated catalyst does not upset the temperature constraints of thereactor operations in a significant amount.

The reactor arrangement of the invention is provided as mentioned abovewith conduit means 18 such as a riser conduit for removing catalyst froma bottom portion of the vessel beneath grid 8 to an upper portion of thevessel for discharge above the bed upper dense phase interface as shown.Conduit means 21 is provided for charging an inert gas such as nitrogenfor use as lift gas for removing catalyst particles by passing asuspension thereof upwardly through riser 18. The top of the riser iscapped, for example, by a dish shaped baffle as shown to reduce flow ofcatalyst down through the riser. Conduit 21 may comprise a verticallymoving plug type valve at the bottom inlet which will be closed whencharging methanol to the chamber beneath grid 8.

The methanol feed with or without nitrogen or another appropriatediluent may be charged through one or more openings 20 and 22 in abottom extended portion of the reactor. The methanol in liquid conditioncan be sprayed by suitable means into the bed above the grid. Thecharged methanol feed in vaporous condition enters the vessel by inletmeans 20 and 22 in open communication with chamber 24 beneath grid 8.The charged methanol passes through reactant distributor grid 8 and intothe bed of catalyst thereabove at a velocity sufficient to form agenerally upwardly flowing suspension of reactant and reaction productwith the catalyst particles. The suspended catalyst in a concentrationgenerally less than 35 lbs/cu.ft. and about 27 lbs/cu.ft. in a specificarrangement is in random fluid movement in the bed by upflowing gasiformmaterial, with a substantial portion thereof moving generally upwardwith the gasiform product material into a more dispersed catalyst phase28 above catalyst bed interface 26.

A plurality of sequentially connected cyclone separator means 30, 32 and34 provided with diplegs 36, 38 and 40 respectively are positioned in anupper portion of the reactor vessel comprising dispersed catalyst phase28. In a specific arrangement, there are eight sets of three stagecyclone separating means providing in an upper portion of the reactorvessel. As shown by FIG. II, provision is made for extending the cyclonediplegs into the dense fluid bed of catalyst and preferably to a bottomportion of the fluid bed for discharge in a vertical space between grid8 and the bottom of tubes 4 and 6 within the bed of about 2 feet. Thusin the reactor arrangement of this invention and the proposed method ofutilization for converting methanol to hydrocarbons comprising olefins,aromatics, paraffins and naphthenes, the operation contemplates a highcirculation rate of catalyst within the reactor vessel. In a specificexample, the reactor catalyst inventory is about 878,500 pounds, andfrom about 4 to 8 million pounds per hour of catalyst are circulatedprimarily through the cyclones. In conjunction with this high catalystcirculation operation, it is contemplated maintaining the followingspecific reactor operating conditions:

    ______________________________________                                        Feed to Grid 8                                                                Methanol, mph           19,785                                                Recycle gas, mph        1,522                                                 Condition below Grid 8                                                        Temperature, °F. 350                                                   Pressure, psig          34.5                                                  Condition above Grid                                                          Temperature, °F. 765                                                   Pressure, psig          32.2                                                  Fluidized Catalyst Bed Depth, ft.                                                                     40                                                    Fluidized Catalyst Bed Density, lbs/cu.ft.                                                            27                                                    Fluidized Bed Pressure Drop, psi                                                                      7.5                                                   ______________________________________                                    

The product effluent of methanol conversion separated from catalystparticles in the cyclone separating system then passes to a plenumchamber 42 before withdrawal therefrom by one or more opening means 44and 46. The product effluent recovered by openings 44 and 46 is cooledand separated in means not shown to recover liquid hydrocarbons, gaseousmaterial and formed water comprising some catalyst fines. Sinceconversion of the methanol is at least 95% and preferably at least 99%,the water phase with unreacted methanol is not processed for economicreasons to recover unreacted methanol. The recovered hydrocarbon productcomprising olefins and/or aromatics, paraffins and naphthenes isthereafter processed as required to provide a desired gasoline or higherboiling product. In the event the reaction conditions selected produceconsiderable materials higher boiling than gasoline such as a light fueloil, the higher boiling material is separated from the gasoline productfor further use as desired. Light gaseous hydrocarbon products of theprocess may be processed as by alkylation, olefination and other knownprocesses to produce gasoline boiling components, LPG, etc.

The total catalyst inventory for the reactor and regenerator (not shown)is about 933,000 pounds based on a 40 foot catalyst bed depth in thereactor. Therefore the regenerator catalyst inventory is about 54,500pounds in a specific embodiment. The catalyst regenerator contemplatedfor use with the reactor system of this invention can be substantiallyany arrangement suitable for the purpose and consistant with providing alow temperature regeneration of the catalyst below 1000° F. to effectonly partial coke removal by burning. Thus a dense fluid catalyst bedregeneration system may be successfully employed. The density of theregenerator fluid bed of catalyst may be the same as, slightly higher orlower than, the reactor bed density. Generally it will be about 27lbs/cu.ft. or slightly higher to provide a proper pressure balancedsystem. In order to restrict the coke burning operation within limitsdesired, the top of the dense bed is preferably restricted not to exceeda temperature of about 900° F. and the regenerated catalyst outlettemperature preferably should not exceed about 950° F. The pressurewithin the regenerator is preferably about 29.9 psig at the base of thefluid bed of catalyst in the bottom portion of the regenerator. Acatalyst bed depth of about 30 feet is proposed for this specificoperation. The incompletely regenerated catalyst particles carrying ahigh level of coke thereon are recovered from the catalyst regenerationoperation not shown and returned to the methanol conversion reactor at arestricted temperature by conduit 14.

Important aspects of the methanol conversion reactor herein describedare manifold, since they include (1) restricting the exothermictemperature generated within relatively narrow limits; (2) restrictingthe reactant vapor bubble growth and thus the hydraulic diameter of theoperation within particular limits; (3) maintaining a catalyst conditionparticularly promoting the formation of olefins and/or aromatics,paraffins, and naphthenes depending on feed composition comprisingmethanol; (4) maintaining a reaction condition promoting greater than95% conversion of the methanol charge to more desirable products becauseof economic consideration as well as product consideration; and (5)maintaining a catalyst circulation system within operating restrictionsabove identified and particularly promoting the conversion of methanolto olefinic and/or aromatic gasoline boiling components.

One of the more important aspects above identified is concerned with theremoval of exothermic heat and restricting the vaporous reactanthydraulic diameter. FIG. II identifies a cross-sectional view A--A ofthe apparatus of FIG. I having a particular bearing on these importantaspects. That is, FIG. II shows the systematic relationship betweenvertically positioned steam tubes 50 shown as black dots with baffletubes 52 at each cross mark to achieve the desired heat exchange andmaintain a desired reactant hydraulic diameter or gas bubble growthrestriction. FIG. II also shows the arrangement of cyclone standpipes54, 56, 58, 60, 62, 64, 66, 68 and 70 provided for accomplishing thecatalyst circulation desired. In each quarter section of the reactorcross-sectional area, there are at least six standpipes for returningcyclone separated catalyst to the fluid bed of catalyst. In addition,the 4 inch diameter tubes, comprising steam tubes and baffle tubes, arespaced on a grid pattern of 6 inch square or pitch which are groupedinto 36 inch square bundles, each typically containing 4 steam tubes and32 baffle tubes. In the reactor design of this invention, there are 352steam tubes and 3,192 baffle tubes. The hydraulic diameter of each 36inch square tube bundle is about 5.3 inches when using 4.5 in O.D. tubesin a specific arrangement. However, the hydraulic diameter of thereactor is about 6 inches.

The baffle tubes 52 used in the apparatus are particularly shown inpartial view in FIG. III. These baffle tubes 52 confined with the densefluid bed of catalyst as herein provided are open ended tubes, about 4inches in diameter or 4.5 inch O.D. tubes, and slotted in the wall asshown to provide approximately 2×4 inch slots to permit ingress andegress of catalyst particles and vaporous material within the bubblebreaking constraints of this invention. For a baffle tube of 4 inchdiameter, the slots are generally round on each end and arranged in apattern in the tube wall throughout a major portion of its length.

FIGS. II and III are believed to be generally self-explanatory whenconsidered in the light of the discussion above and minor deviationstherefrom are considered to be within the scope of the invention.

Having thus generally described the method and apparatus of thisinvention and described specific examples in support thereof, it is tobe understood that no undue restrictions are to be imposed by reasonsthereof except as defined by the following claims.

We claim:
 1. An apparatus for converting lower alcohols to hydrocarbonsincluding gasoline boiling range hydrocarbons which comprises, incombination, an elongated substantially vertical cylindrical reactorvessel, a horizontal grid means positioned across a bottomcross-sectional portion of the vessel above a bottom semicircularclosure member of the vessel,a plurality of vertical heat exchangertubes positioned within a lower portion of the vessel with the bottom ofthe tubes spaced vertically above the grid means, a plurality ofvertical open end baffle tubes slotted in the wall thereof throughoutsubstantially the entire length thereof positioned interspersed with andadjacent to said heat exchange tubes and spaced horizontally from oneanother and from said heat exchange tubes to maintain a reactanthydraulic diameter of less than 24 inches during contact with a fluidmass of catalyst particles, the bottoms of said baffle tubes spacedvertically above said grid means, conduit means for withdrawingparticles of catalyst from the space intermediate the grid means and thebottom of said tubes, conduit means for adding particles to an upperportion of a bed of fluid catalyst in which said heat exchange means isimmersed, a plurality of cyclone separating means located in an upperportion of said vessel provided with dipleg means extending downwardthrough said vessel and terminating in the space above said grid means,a plenum chamber in the upper portion of said vessel in opencommunication with said cyclone separating means and conduit withdrawalmeans for reaction products connected to the upper portion of saidplenum chamber, an open end conduit means extending from a bottomportion of said vessel beneath said grid means to an upper level of saidvessel above said heat exchange and baffle tubes and terminating abovethe upper interface of a fluid bed of catalyst in the lower portion ofthe vessel, means for introducing separately controlled gases to thebottom of said open end conduit means, means for charging reactant tosaid vessel beneath said grid means for flow upwardly through saidvessel.
 2. The apparatus of claim 1 wherein the vertical heat exchangetubes and said open end slotted baffle tubes are sized in diameter andhorizontally positioned with respect to one another to maintain ahydraulic diameter relationship therein within the range of 4 to 8inches during contact between vaporous material and fluid particles ofcatalyst.
 3. The apparatus of claim 1 wherein the vertical heat exchangetubes are separated into a plurality of tube bundles which can beseparately controlled for flow by liquid therethrough or removal fromsaid vessel.
 4. The apparatus of claim 1 wherein the tubes are 4 inchdiameter tubes and the axis of the tubes is aligned with the cross marksof a 6 inch grid pattern in the vessel cross-section.
 5. The apparatusof claim 1 wherein the tubes are grouped into 36 inch square bundles,each bundle comprising 4 steam tubes and 32 baffle tubes.